The present invention relates to a magnet pump with bi-directional axial self-alignment. More particularly, the present invention relates to a magnetic entraining pump suitable to support and counterbalance axial thrusts in both directions and to keep the impeller in the exact position even in extreme or abnormal operating, conditions.
Magnet pumps are commercially well known and described in the literature, such as for instance in British Patent No. 1,134,228. Magnet pumps are typically centrifugal, one-step pumps, with a preferably closed impeller and are employed in liquid pumping, including in chemical and corrosive applications, in water purification and recovery, and in conjunction with heat exchangers, sea water desalination plants, etc.
Generally, magnet pumps include an inner chamber having, a suction duct that extends axially and a delivery duct that extends circumferentially; an impeller located inside of the chamber so as to be capable of rotating therein, and possibly translating axially. The impeller has a front side, oriented towards the suction duct, and a rear side, oriented in the opposite direction; a driving rotor, located outside the chamber, fixed to a motor spindle and provided with driving magnets; a driven rotor, fixed to the impeller and provided with driven magnets that face onto, and form a magnet coupling with, the driving magnets, and thrust-bearing front and rear bushings, located between the walls of the chamber and, respectively, the front and rear sides of the impeller.
During operation, the magnet pump takes in the fluid to be transferred through the suction duct and drives it towards the delivery duct through the action of the impeller. During, this action, a pressure drop is created on the front side of the impeller that faces the suction duct; while the impeller and the driven rotor receive a thrust in the direction towards the suction ducts. These actions create a thrust oriented towards the suction duct on the impeller, the thrust being contrasted by the front thrust-bearing bushing.
In particular pressure conditions, the impeller may also translate in the opposite direction, causing the impeller guide bushing to get in touch with the rear thrust-bearing bushing. The pumped liquid also functions to dissipate the heat that is generated due to the friction between the impeller and the thrust-bearing bushings, as well as functions to lubricate the bushings, thereby ensuring proper operation over a long duration of time.
In critical or abnormal operating situations, such as in the case of cavitation (the absence of liquid flow through the pump, or the presence of excessive amounts of entrained gases in the liquid), an excessive vibration phenomenon develops, and because of the presence of gas bubbles in the fluid intake, there is little axial thrust on the impeller and the functions of dissipation of frictional heat and lubrication of the moving parts of the pump are performed by the pumped liquid. In such conditions, as the impeller cannot be maintained any longer in its operating position abutting the front thrust-bearing bushing, it may translate along a supporting spindle and contact the rear thrust-bearing bushing, causing the ensuing generation of more friction heat. The heat thus developed can no longer be dissipated and may lead to severe damage to the pump and even to its seizure and resultant total working failure. Additionally, this type of magnet pump cannot function at idle, that is, in the absence of circulating fluid, for long periods, as that would result in severe damage to the pump for the above-stated reasons.
It is apparent that the aforementioned drawbacks and limitations are unacceptable in magnetic entraining pumps, not only because they may lead to a complete failure of operation of the unit, but especially in the context of their operation in the handling of liquid chemicals, where possible interruptions in operation may prove to be particularly damaging and deleterious to the extent of causing unacceptable risks to both persons and facilities.
Various devices have been proposed to obviate the above drawbacks, however, heretofore none of them has completely solved all of the problems in a satisfactory and economical manner. Thus, for instance, it has been proposed to employ a structure made from thermal insulating, material to enclose the portion of the thrust-bearing bushing most susceptible to frictional heat damage.
This solution, in addition to being expensive, also involves exposure to high temperatures at the contact points, since the insulating characteristics of the material prevent any diffusion of heat, which, even for short periods may lead to the occurrence of so-called xe2x80x9cthermal shockxe2x80x9d.
It has been also proposed to employ thrust-bearing devices constituted by push rods having a rounded end to counteract any axial shifting of the impeller. This solution is also not free from drawbacks since such devices still involve the occurrence of a sliding contact.
Accordingly, it is an object of the present invention to overcome the foregoing drawbacks. More particularly, it is an object of the present invention to provide a magnetic entraining pump that is capable of operating under any set of conditions, and to prevent the onset of heat or an increase in temperature due to frictional contact, even in extreme or abnormal operating conditions.
In its most general aspects, the present invention allows the achievement of these and still other objects, which will be apparent from the following description, by providing a magnetic entraining pump wherein the impeller is kept in stable equilibrium and its axial position is controlled and self-aligned in both directions. This is achieved by counteracting the axial thrusts and pressures, which the pump impeller is subjected to, by means of a linear magnetic coupling between the impeller and the chamber wherein the impeller is located.
A magnetic entraining pump according to the present invention comprises an inner chamber, preferably cylindrical, provided with a suction duct that extends axially and a delivery duct that extends along the circumference; an impeller located inside of the chamber and having a front portion oriented towards the suction duct, a rear portion oriented towards the opposite direction, and a central support portion; a cup-shaped driving rotor, located outside the chamber and having at least a driving magnet; a driven magnet fixed to the impeller and that faces onto and forms a magnetic coupling with the driving magnet; a supporting spindle that extends axially in the chamber and that supports the impeller in a rotatably and axially movable manner, and, optionally, front and rear thrust-bearing bushings located on the spindle adjacent to the front portion and the rear portion of the impeller, wherein both the chamber and the impeller are provided with at least a magnet and the respective magnets are mutually aligned and arranged such that opposite poles are adjacent to one another, so as to form a linear magnetic coupling when the impeller is in a position of equilibrium between the two front and rear thrust-bearing bushings.
The magnets are arranged such that opposite poles are adjacent to one another, i.e. the North pole of one magnet concatenates with the South pole of another magnet, and vice-versa, so that the opposite poles mutually attract, forming a linear magnetic coupling that keeps the impeller in a position of stable equilibrium. The magnetic coupling opposes any axial force or thrust that tends to alter conditions of equilibrium and perfect alignment of the magnets. Therefore, any axial shifting of the impeller is prevented, as it involves the creation of an opposite return force, and the amount of such a return force increases as the misalignment between adjacent magnets increases.
The thrust-bearing bushings may be of the mechanical type or, especially in the presence of very high axial thrusts, may be, at least partly replaced by thrust-bearing bushings of the magnetic repelling type, which comprise magnets aligned and located in the impeller and the front and/or rear walls of the chamber with like poles opposite to one another, i.e. with the North pole of one magnet opposed to the North pole of another magnet and vice-versa, so as to generate a repelling magnetic force.
The characteristics of the construction and function of the magnetic entraining pump of the present invention are better understood from the following detailed description, wherein reference is made to the figures of the attached drawings, which illustrate a preferred embodiment of the invention, which is presented solely as a non limiting example.